Syntheses and structures of di(carboxylato)hexakis(acetonitrile)-dimolybdenum(II) bis(tetrafluoroborate) and trans-[di(μ-acetato)-di(acetonitrile)di(μ-bis(diphenylphosphino)amine)dimolybdenum(II)] bis(tetrafluoroborate)

Abstract

Di(carboxylato)hexakis(acetonitrile)dimolybdenum(II)bis(tetrafluoroborate)s, [Mo 2(μ-O 2CR) 2(CH 3CN) 6](BF 4) 2 (R = CH 3, CH 2Cl, C(CH 3) 3, CF 3) ( 3a-d), are easily accessible by reacting [Mo 2(CH 3CN) 8](BF 4) 4 ( 2) with a stoichiometric amount or a slight excess of the appropriate carboxylic acid and anhydride in acetonitrile. A large excess of carboxylic acid leads to the formation of tetracarboxylates. As an example cis-[Mo 2(μ-O 2CCH 2Cl) 2(CH 3CN) 6](BF 4) 2 ( 3b) has been structurally characterized. Crystallographic data are as follows: space group: I42 d (No. 122), a = b = 10.733(2), c = 59.448(5) A ̊ , V = 6848(2) A ̊ 3, Z = 8, d( Mo-Mo) = 2.140(1) A ̊ . Trans-[Mo 2(μ-O 2CCH 3) 2(dppa) 2(CH 3CN) 2](BF 4) 2 ( 4) can be synthesized from cis-[Mo 2(μ-O 2CCH 3) 2(CH 3CN) 6](BF 4) 2 ( 3a) and bis(diphenyl-phosphino)amine (dppa) at room temperature. This result contradicts earlier reports where bulky diphosphines such as dppm (sterically very similar to dppa) did not lead to bis-diphosphine products. Furthermore our results indicate that in all the syntheses reported to date for [Mo 2(μ-O 2CCH 3) 2(LL) 2](BF 4) 2 type-compounds [Mo 2(μ-O 2CCH 3) 2(CH 3CN) 6](BF 4) 2 acts as the precursor compound. Crystallographic data for 4 are as follows: P2 1/ c (No. 14), a = 19.683(3), b = 15.129(2), c = 21.084(1) A ̊ , β = 101.30(1)°, V = 6848(2) A ̊ 3, Z = 4 . There are two independent molecules of the cation in the unit cell, d( Mo-Mo) = 2.133(1) and 2.136(1) A ̊ .